[actuator] Improve a bit documentation and style
[core] Copy the doc in the decorated async function

It permits to build useful doc for asynchronous service
[doc] Don't replace \n by '' but by space
[doc] Generate automatically documentation for rotorcraft_waypoint
[doc] Use automatically generated doc for more components
[doc] Link component doc to source file and unit-test file
[builder] fix empty_add is new in 2.65